1. Field of the Invention
The present invention relates to a semiconductor laser used, for example, as a light source of an optical disc apparatus, in particular to a ridge-stripe semiconductor laser.
2. Related Art
Among semiconductor lasers, semiconductor lasers made of a III-V nitride semiconductor material (e.g. AlxGayIn1-x-y (provided that 0≦x≦1, 0≦y≦1)) are especially being developed to a practical level as a key device for a realization of super high density recording of optical disc apparatuses.
Some semiconductor lasers have a configuration in which an n-type cladding layer 902, an active layer 904, and a p-type cladding layer 907 are formed in layers on a substrate 901, and a ridge is provided with the laminated composite, as shown in FIG. 9. A semiconductor laser 900 formed in this manner emits laser light outward according to the injected current (i.e. carriers) from a p-type electrode 921 covering the ridge and an n-type electrode (not shown) disposed on the underside of the substrate 901. At this point, since a region into which current is injected is limited only to the apex portion of the ridge by the insulating layer 910, a gain distribution occurs inside the semiconductor laser 900 and thereby a waveguide mode is formed. Thus, by increasing the carrier density in the active layer 904 and confining light, efficient laser light emission is realized.
In addition, of a pair of films 931 and 932 disposed at both ends of the laminated composite in a manner that they oppose each other along a direction substantially perpendicular to the stretching direction of the ridge (Z direction), one 931 (hereinafter, “front film”) is set to have a spectral reflectance of 10% and the other 932 (“rear film”) is set to have a spectral reflectance of 90% so as to form a resonator structure that emits laser light from the front film 931 in a concentrated manner. Herewith, the output of the light emitted from the semiconductor laser 900 in the forward direction is enhanced.